dear experts
In NB-3122.2 design dimensions, clearly said that:

The dimensions given in (a) and (b) below shall be used in the design of the component:
(a)For component subjected to internal pressure, the inside diameter shall be taken at the nominal inner face of the cladding.
(b)For components subjected to external pressure, the outside diameter shall be taken at the outer face of the base metal.

I can not understand the above two sentences:
For (a), if vessel subjected to internal pressure, then the cladding will be built-up by welding onto the inside surface of vessel. The "nominal inner face of the cladding" means where? Is it the interface location between cladding and base metal or not?

For (b), if vessel subjected to external pressure, then the cladding will be built-up by welding onto the outside surface of vessel. The "outer face of the base metal" means where? Is it the interface location between cladding and base metal?